BackgroundVenoplasty—dubbed the liberation procedure—has been proposed with the controversial theory of chronic cerebrospinal venous insufficiency (CCSVI), as a possible treatment for multiple sclerosis. Despite concerns about its effectiveness and safety, thousands of patients have undergone this procedure. Those with positive results often become vocal advocates and use internet technologies to express their support. In the extant published work, social media is both credited and criticised as affecting research and policy decisions. However, no in-depth analysis has been done of how internet technologies are actually being used in this context. MethodsFrom more than 4000 videos returned from a YouTube search for CCSVI, we used a mixed methods approach to analyse the top 100 most viewed. 70 videos remained after non-English language and non-CCSVI videos were removed. First, with an inductively derived coding scheme, in which all three authors independently coded the first 15 videos and reached a consensus as to what constituted a positive, negative, or ambiguous video. BGO'N and FM independently coded the videos in terms of topic and attitude adopted towards CCSVI: negative, positive, neutral, or ambiguous. Second, a qualitative analysis was done on channels incorporating patients' experiences before and after venoplasty. FindingsThe videos adopt an overwhelmingly positive stance towards CCSVI (67, 96%); 46 (66%) of them were uploaded by patients, most of which present treatment experiences before and after venoplasty (26, 57%). These videos are popular, with the number of views of the top 100 videos ranging from 7103 to 79 956. These figures are similar to those for videos about another alternative treatment, low-dose naltrexone (1332–131 141) and a biomedically accepted one, natalizumab (3911–72 595). They are also consistent with those for the top 100 videos about human papillomavirus (10–43 172). We identified three subtypes of patient video. The first, commercial patient experience, focuses on individual patients, but is produced and circulated by a third party for promotional purposes. The second, personal treatment evidence, focuses narrowly on the liberation procedure and has one or two videos of before and after venoplasty directly linked to treatment. The third, experiential diary, includes diaries and commentaries on living with multiple sclerosis or CCSVI, or both. Some of these channels span years and have more than 30 videos, combining discussions on CCSVI and multiple sclerosis with other aspects of the individual's life. They contain strong advocacy messages, using the patients' experiences to call for venoplasty to be funded and supported as a treatment for multiple sclerosis. InterpretationYouTube allows patients to vividly show and describe the effectiveness of treatments. Social media platforms enable the aggregation of individual experiences, creating a database of experiences that patients can draw on in making their decisions and use when advocating policy changes. The increasingly mainstream adoption of social media technologies means that this type of so-called people power advocacy, in which patients turn personal experience into a form of evidence, will probably proliferate and be adopted by other groups looking to disseminate their message. In the case of CCSVI, this use of social media technologies has led to some patients expressing frustration at the slow speed of research and policy change, whereas many in the medical establishment have expressed an equal frustration about what they perceive as a hijacking of the multiple sclerosis research agenda—so-called pester power. This study highlights some of the tensions that practitioners and policy makers face as patients go online, not only to seek information, but also to share it. FundingUK National Institute for Health Research.